Abstract: The marine shale source rock system has the high-temperature pyrolysis gas-sourcing ability in the later period. Take for examples the Cambrian Qiongzhusi Formation and Silurian Longmaxi Formation in the Yangtze area and the Changcheng-Qingbaikou Xiamaling Formation in North China area. The gas-sourcing potential of marine mud shale source rock in the later period is brought under study on the basis of the closed system and the open system to determine whether marine mud shale has the high-temperature pyrolysis gas sourcing ability in the later period. Two parameters – LGP and LGT – are used to evaluate the high-temperature pyrolysis gas-sourcing ability. The thermal development process of gas from source rock is a very complicated process. When thermal pyrolysis hydrocarbon sourcing takes place, a certain quantity of melting-resistant molecule – NSOs – is generated from condensation polymerization. NSOs is cracked into hydrocarbon gas under the high-temperature development stage. The rock pyrolysis experiment shows that the samples of source rock from Qiongzhusi Formation and Longmaxi Formation can produce heat-cracked hydrocarbons under the high-temperature development stage. For example, SP-1 can still produce 0.092mg/g (HC/TOC) after R_o =2.42%, indicating that source rock can still keep the sourcing ability under the hightemperature development stage, but the sourcing efficiency is low. The LGP - LGT standard is used to evaluate the gas-sourcing ability of marine mud shale in the later period. LGT of the inspected marine mud shale is >1, indicating the ability to produce high-temperature cracked gas of B type in the later period. LGP is distributed between 0.51 and 0.55, indicating the medium-level potential for high-temperature cracked gas. The average potential of inspected samples for high-temperature cracked gas is 2.6 mg/g (HC/TOC), belonging to the relatively low natural gas productivity. Based on calculation, it is about 0.2 m³/t (HC/rock). Take shale from the Silurian Longmaxi Formation in China^’s Shunan area for instance. The actually inspected gas content is about 3m³/t (HC/rock). The high-temperature cracked gas will account for 6.7 percent.